Plant Biotechnology Laboratory, School Of Molecular And Cell Biology, University Of The Witwatersrand
Post-Doctoral Fellows - 2 Positions available
Start Date: 2019
REQUIREMENTS: Both postdoctoral positions require the appropriate qualifications and should preferably be South African permanent residents or citizens, but this is not an absolute requirement. The background required to do this project would be microbiology (preferably some plant virology); molecular biology; and some plants genetics and plant biology background. Basic bioinformatics is also required.
Applications or enquiries should be sent by email along with three reference contacts (with email contacts); CV; copy of ID and academic transcripts.
FUNDING: NRF Blue Skies/SA-India Bilateral Grant/Leap -Agri
CONTACT: Professor Chrissie Rey
PROJECT 1: Characterization of genes conferring natural resistance against cassava geminiviruses
Cassava is an important food security crop and source of starch for industrial applications and biofuels. Cassava mosaic disease (CMD), caused by cassava mosaic geminiviruses (CMGs) and transmitted by whitefly Bemisia tabaci Gennadius, is one of the two most important viral diseases of cassava in Africa. There are arguably only two approaches to controlling or reducing virus disease and preventing crop yield losses: genetic engineering using a pathogen-derived approach which induces basal innate immunity (RNA silencing); or to mine natural genes that are involved in susceptibility or resistance in crops, such as cassava, and use those to manipulate the host plant. Our laboratory is interested in exploring new aspects to host-pathogen interactions which will help to devise strategies for managing or reducing crop losses.
Dominant resistance genes against geminiviruses have so far been characterized in Fabaceae and Solanaceae species. Cassava represents another potential source of resistance against geminiviruses, in particular a CMD2 locus that has recently been mapped to a ~2 Mbp genomic region of chromosome 12. Additionally other putative candidate immunity-related genes have also been identified.
We intend to further advance our understanding of CMD resistance by identifying the gene(s) associated with CMD2 and CMD3 loci on chromosome 12, and other putative candidates. Gene validation will be performed in cassava, taking advantage of genetic platforms available in the consortium as well as the ACMV-based Virus Induced Gene Silencing (VIGS) tools; high throughput CRISPR gene editing; and RenSeq available in the Rey laboratory and those of Gallois and Vanderschuren (collaborators).
PROJECT 2: STRUCTURAL AND FUNCTIONAL ANALYSES OF GEMINIVIRAL PROTEINS
The family Geminiviridae includes economically important plant viruses that infect either monocotyledonous or dicotyledonous plants. All are transmitted in a circulative, persistent, non-propagative manner by arthropod vectors. In 1978 the International Committee on taxonomy of viruses recognized geminiviruses as a distinct family on the basis of the possession of circular ssDNA and having unique geminate virion morphology. The genomes of these viruses are composed of one or two ssDNA components that each range in size from 2.5 kb to 3.1 kb. Geminiviruses are the best characterized plant viruses because of their small genome size, availability of vectors and easy manipulation by molecular approaches due to having DNA genomes. These viruses are found in tropical, sub-tropical and temperate areas of the world and have spread due to environmental changes and human trade. The genus Begomovirus is the largest in the family Geminiviridae, containing more than 300 species, and is economically the most destructive, causing disease of many crops including subsistence crops such as cassava in Africa. Currently in South Africa the begomoviruses, South African Cassava Mosaic Virus and Tomato curly stunt virus (ToCSV) are severely affecting the production of cassava and tomato, respectively. ToCSV exhibits symptoms similar to Tomato yellow leaf curl-disease while SACMV produce mosaic symptoms on leaves. Two strains (mild and severe) have also been found associated with tomato curly stunt disease.
The replication-associated protein (Rep) is a ~41 kDa protein encoded in the complementary-sense orientation by all geminiviruses. While the functions of Rep are known, little structural analyses have been done on the tertiary or molecular structure of this multifunctional protein. The present study will be conducted with the aim to better understand the role of begomoviruses encoded Rep and other proteins in disease etiology of commercially important crops, cassava and tomato. A more in-depth knowledge of the begomoviruses encoded proteins may allow us to design better control strategies.
- a) Structural determination of SACMV Rep of cassava [and compare with ToCSV Rep in tomato (project already underway)]
- b) Role of ToCSV Rep mutations in severe and mild symptom phenotypes: analysis of the effects of mutations on pathogenicity and suppression of post-transcriptional gene silencing activity